Surgical tourniquet cuffs typically are applied to a patient's limb at a desired location and are then pressurized in order to stop the flow of arterial blood past the cuff, thereby establishing a bloodless filed in the portion of the limb distal to the cuff. The structure and function of some typical tourniquet cuffs of the prior art are described by Robinette-Lehmann in U.S. Pat. No. 4,635,635, by Spence in U.S. Pat. No. 4,979,953 and by McEwen in U.S. Pat. Nos. 5,454,831 and 5,649,954. The pressure applied by such prior-art tourniquet cuffs is typically controlled by electronic tourniquet apparatus such as that described by McEwen in U.S. Pat. No. 4,469,099 by McEwen and Jameson in U.S. Pat. No. 5,607,447.
The bloodless surgical field created by a pressurized tourniquet cuff facilitates many types of surgical procedures performed on upper limbs and lower limbs, helps improve the quality and consistency of the surgical procedures, reduces the need for blood transfusions, and shortens surgical times. In certain kinds of surgical procedures, only the portion of the limb distal to the tourniquet cuff is anesthetized using a procedure called Bier block anesthesia or Intravenous Regional Anesthesia (IVRA); in such procedures, the tourniquet cuff performs a dual function of keeping the anesthetic agent in the limb and keeping arterial blood out of the limb. Clinical practice involving the use of tourniquets in IVRA was recently summarized in a paper by Henderson et al. entitled “A North American Survey of Intravenous Regional Anesthesia” published in Anesthesia and Analgesia (1997; 85:858-863).
In an effort to reduce the probability of certain injuries to the soft tissues of the limb beneath a pressurized tourniquet cuff, some operators may elect to apply a soft bandage to the limb beneath the cuff. For example, in “Recommended Practices for Use of the Pneumatic Tourniquet”, published by the Association of Operating Room Nurses (AORN) in the United States and effective as of Jan. 1, 1999, it is noted that “The cuff should be applied to the extremity so that underlying skin and soft tissue are not unduly traumatized. Manufacturers' instructions may suggest that a soft, wrinkle-free padding (eg, cotton cast padding, stockinette) be wrapped smoothly around the limb as high on the extremity as possible, being careful not to pinch the skin folds where the tourniquet is applied. Once inflated the cuff should not be readjusted. Users must note that some tourniquet technology does not require padding.”
In the prior art, soft bandages that have been used in conjunction with tourniquet cuffs have included sheet padding combined with a fluid-impervious layer and an adhesive tab as described by Hubbard et al. in U.S. Pat. No. 4,406,281, as well as cast padding of the type wrapped around a broken limb before a cast is applied. Proper application of these soft bandages in conjunction with tourniquet cuff usage is very technique-dependent, requiring a trained and experienced applicator. Further, some types of padding may release loose fibers when applied, and these fibers may enter the surgical field and may clog the hook-and-loop fasteners that are typically used to secure tourniquet cuffs in position around the limb, thereby reducing the effective strength of these fasteners and creating a potential hazard. Also, the padding itself may take on a non-uniform shape around the limb, especially when an overlying tourniquet cuff is inflated. Finally, if too much soft bandage is used or if it is applied improperly, then hazards may arise because the level of pressure required in the tourniquet cuff to stop blood flow past the cuff may increase substantially, and the position of the cuff on the limb may become unstable after inflation, increasing the likelihood that the cuff position may change significantly relative to the limb during use.
An alternative to the use of soft bandages and cast padding in the prior art has been to use tubular stockinette between the patient's limb and the tourniquet cuff. Typically, tubular stockinette is made and supplied in a wide range of predetermined ‘lay-flat’ widths, knits and materials. Tubular stockinette consists of a knitted textile having a substantially cylindrical shape in which some of the knitted threads either are elastic or are knitted in a manner that permits elastic stretching of the tubular shape. In appearance, tubular stockinette resembles the ankle portion of a sock or the leg portion of a nylon stocking. Elastic threads are included in some types of tubular stockinette to give them stretch and elastic characteristics that are a function of the type and number of elastic and non-elastic threads used in the knit and the knit pattern itself. In other types of stockinette that are knitted from non-elastic threads, the stretch and elastic characteristics of the stockinette are primarily determined by the type of knit. Two general advantages of using tubular stockinette under a tourniquet cuff, in comparison to overlapping soft bandages, are: tubular stockinette does not shed loose fibers which can enter the surgical field and clog cuff fasteners; and tubular stockinette does not produce as non-uniform a shape around the limb as soft bandages may do.
There are a number of limitations associated with such prior-art tubular stockinette. The most important limitation is that the pressure applied to the encircled limb by the tubular stockinette may be too high or too low. If the tubular stockinette is stretched excessively to fit around the limb at the desired cuff location, too high a pressure may result: in such situations, the pressure applied to the limb by the elastically stretched tubular stockinette may be sufficiently high to stop the flow of venous blood out of the limb and impair the flow of arterial blood into the limb.
Because of the concern about residual pressures that might be applied by tubular stockinette, one manufacturer of prior-art tourniquet cuffs and instruments (Zimmer, Warsaw Ind.) cautions on page 6 of the Operator and Service Manual for its A.T.S. 2000 Automatic Tourniquet System that “As an under padding, a section of stockinette may be used. The deflated cuff and any underlying bandages should be completely removed as soon as tourniquet pressure is released. Even the slightest impedance of venous return may lead to congestion and pooling of blood in the operative field.” Similar cautions and warnings about hazards related to the residual application of non-pneumatic pressure by underlying padding such as stockinette, as well as tourniquet cuffs, are given by other suppliers of tourniquet-related products and in the surgical literature.
Alternatively, if the tubular stockinette is not stretched at all, or if it is not stretched sufficiently at a desired cuff location, then the tubular stockinette may apply no pressure to the underlying limb and inflation of an overlying tourniquet cuff may then produce folding and wrinkling of the tubular stockinette material. This can cause soft tissue injuries resulting from pinching, folding and shearing of skin beneath the tubular stockinette, as well as causing other hazards arising from local anomalies in the pressure applied to the limb beneath the tubular stockinette by the inflated cuff and from the increased inflation pressure that may be required in the cuff to stop blood flow.
One commercial product is known in the prior art that combines tubular stockinette and a single-use tourniquet cuff in a single sterile package (Smith and Nephew Richards Inc., Memphis Tenn.). The tubular stockinette consists of a substantially cylindrical length of elastically stretchable knitted fabric that has been folded back on itself twice, so that by pulling the tubular stockinette up a limb to a desired cuff location, the tourniquet cuff can be applied over four layers of stockinette material. In products inspected by the inventor one common sleeve size was supplied with the 12″ and 15″ cuff sizes, thus that specific sleeve is not matched to a specific cuff, but to two cuffs of differing sizes for differing limb circumference ranges. Similarly, a second common sleeve size was supplied with the 24″, 34″, and 44″ cuff sizes. The instructions enclosed with the cuff specify that the user should select a cuff large enough to have at least a suggested three-to-four inch overlap. In practical use, if the overlap is less than the suggested three-inch minimum at a desired limb location with a selected cuff, then the next larger cuff supplied by the manufacturer must be used. Thus the minimum limb circumference for that next larger cuff is effectively equal to the limb circumference that creates less than a three-inch overlap in the selected cuff. Accordingly, the effective limb circumference range of each cuff is (a) a maximum that allows a three-inch overlap, and (b) a minimum that would allow a three-inch overlap in the next smaller cuff. Over part of these ranges, the stockinette sleeves provided with some of the cuffs inspected are too large, i.e. the circumference of the unstretched stockinette is greater than part of the range of circumferences of limbs on which the cuff may be applied. This is hazardous because, as noted above, the inventor has discovered that if the tubular stockinette is loose and not elastically stretched to apply a small pressure greater than a non-zero pressure threshold (determined in testing by the inventor of the present invention to be the minimum pressure at which a visible reduction in wrinkling and pinching was observed) at the desired cuff location on a limb prior to application of the tourniquet cuff, then the application and inflation of the cuff over the stockinette will produce folding and wrinkling of the underlying stockinette material, increasing the likelihood of soft tissue injuries due to pinching, folding and shearing of skin beneath the stockinette, as well as creating other surgical and IVRA-related hazards arising from local anomalies in the pressure applied to the limb and from the higher pressures that must be applied onto such stockinette by the encircling tourniquet cuff to stop blood flow in the underlying limb.
Another similar commercial product is known in the prior art that combines tubular stockinette and a single-use tourniquet cuff in a single sterile package (‘Color Cuff II’, Instrumed Inc., Woodinville, Wash.). The tubular stockinette consists of a substantially cylindrical length of elastically stretchable knitted fabric that has been folded back on itself once forming a two layer stockinette sleeve. However, as with the Smith and Nephew Richards product of the prior art, the sleeves supplied with some of the cuffs are not stretched on some limbs within the size range of the corresponding cuff. Also as with the Smith and Nephew Richards product of the prior art, a sleeve of the same size, and therefore having exactly the same unstretched circumference, is supplied with both the 24″ cuff and the 34″ cuff. Thus that specific sleeve is not matched to a specific cuff, but to two cuffs of differing sizes for differing limb circumference ranges. Instrumed also provides three different sizes of stockinette sleeves, each having a different circumference, for use with the six different sizes of non-sterile reusable tourniquet cuffs that it supplies. However no indication is given in the documentation supplied to users of the cuffs of any correspondence between the sleeve sizes and cuff sizes, and no means is provided for users to match any specific sleeve sizes to any specific cuff sizes.
The pressure applied by a tubular stockinette to a limb of a given shape, circumference and tissue composition can be measured using a biomedical pressure transducer such as the one described by McEwen in U.S. Pat. No. 4,869,265. Using such a transducer, it is has been found in tests conducted by the inventor that pressures from 0 mmHg to more than 60 mmHg can applied to limbs of varying circumferences and physical properties by prior-art tubular stockinettes of varying sizes, materials, knits and designs. For comparison, it has been found that an applied pressure as low as 30 mmHg can partially or completely obstruct venous blood flow, and that applied pressures lower than 60 mmHg can impede and partially block arterial blood flow. It is has been found in tests conducted by the inventor of the present invention that the pressure of a snugly applied tourniquet cuff can be as high as 25 mmHg.
With both the Smith and Nephew Richards and Instrumed products of the prior art, each different cuff size is indicated by a distinct color on the product label and on features permanently attached to the cuff. The sleeves, however, do not have any color or other matching or indicating features permanently attached. Once the sterile package is opened and the cuff and sleeve are separated, there is no indication to the user of the correct matching between the cuff and sleeve. This can be hazardous. For example, in one Smith and Nephew Richards product inspected by the inventor, an apparently incorrect sleeve size was included in the sterile, sealed package. Testing conducted by the inventor (as described in the preceding paragraph) revealed that at the maximum limb size accommodated by the cuff, the sleeve included in the package was extremely tight and applied a hazardous pressure to the limb. In this case, indicating means permanently attached to the sleeve may have alerted the user of the inappropriateness of the sleeve for the limb sizes accommodated by the cuff.
In the prior art, there is no known limb protection sleeve that matches a specific tourniquet cuff for application to limbs having circumferences between a minimum and a maximum circumference so that the sleeve, after application to a limb of minimum circumference, stretches elastically to apply a small pressure greater than a non-zero threshold to the limb that is effective in reducing wrinkling and pinching of the limb, and so that the sleeve, after application to a limb of maximum circumference, applies a pressure to the limb that is less than a predetermined maximum pressure.